Hydraulic variable pitch propellers



March 13, 1962 J. A. cHlLMAN ET AL 3,024,848

HYDRAULIC VARIABLE PITCH PROPELLERS Filed Sept. 50, 1957 5 Sheets-Sheet1.

/ff im m/l l www March 13, 1962 J. A. CHILMAN ET AL 3,024,848

HYDRAULIC VARIABLE FITCH PROPELLERS Filed Sept. 30, 1957 5 Sheets-Sheet2 March 13, 1962 J. A. CHILMAN ET AL 3,024,848

HYDRAULIC VARIABLE FITCH PROPELLERS Filed Sept. 30, 1957 5{Sheets-Shea?l 3 March 13, 1962 J. A. cHlLMAN ET AL 3,024,848

HYDRAULIC VARIABLE FITCH PROPELLERS Filed sept. so, 1957 5 sheets-sheet4 fA/VENTDR Z/ Z/ Z/C JOHN ALFRED @MAMAN er AL BY WMM/ny VMM-12? 4T TVIMarch 13, 1962 J. A. CHILMAN ET AL 3,024,848

HYDRAULIC VARIABLE FITCH PROPELLERS Filed Sept. 50, 1957 5 Sheets-Sheet5 INVENTDR JOHN /H- FRED OHILMAN far/*L BY MMV-)H ATTYS.

3,024,848 HYDRAULIC VARIABLE FETCH ERUPELLERS John Alfred Chilrnan andllvor Harold Broolring, Gloucesn ter, England, assignors to RotolLimited, Gloucester, England, a British company Filed Sept. 3d, 1957,Ser. No. 687,2ll4 Claims priority, application Great Britain .iuly19,1957 18 Claims. (Cl. 17d-160.32)

This invention relates to hydraulic variable pitch propellers. Theinvention is concerned with a hydraulic variable pitch propeller havinga pitch change motor for changing the pitch of the propeller and atleast two line pitch stops which prevent pitch lining movement beyondrespectively first and second line pitch settings and two wihdrawalmeans operable respectively to render the pitch stops inoperative.

An object of the invention is to provide a hydraulic system for thepropeller which overcomes the unreliability that occurred when Ybothwithdrawal means are operated by pressure in a single hydraulic conduit.Accordingly the invention provides two separate conduits respectivelyconnecting the withdrawal means to a source of hydraulic pressure for`operation thereby.

Other objects and features of the present invention will be furtherexplained, or will become apparent from the following descriptions ofspecific embodiments of the present invention which are given merely byway of example, and with reference to the accompanying drawings. In thedrawings:

FlGURE 1 is a diagrammatic illustration of an electrohydraulic controlsystem of a propeller according to the present invention,

FIGURE 2 shows a modification of the control system shown in FIGURE l,

FlGURES 3 and 4 .are electrical circuit diagrams,

FIGURE 5 is a diagrammatic sectional view of a propeller of theinvention,

FIGURE 6 is a detail of `a modified propeller of the invention, and

FIGURE 7 is a detail of FIGURE l to a larger scale and partially inisometric view.

Referring to FIGURE 5, the propeller comprises a rotating hub, part ofwhich is indicated at 11, the hub carrying propeller blades 12 which areadjustable as to pitch angle by a double lacting hydraulic pitch changemotor 14 comprising a ram 15 and cylinder 16 housed in the hub. Finepitch iiuid conduit means 48 is provided extending, from a hydraulictransfer muff denoted X-X (see FIGURE l) through the hub 11 for leadinghydraulic iiuid to `and from the fine pitch side of the pitch changemotor 14, and coarse pitch fluid conduit means Sti is also providedextending through the hub from the transfer muti X-X to the coarse pitchside of the pitch change motor to lead hydraulic iuid to `and from thecoarse pitch side of the pitch change motor. As will readily beunderstood, when hydraulic fluid under pressure is supplied through theconduit means 48 the pitch change motor is operated to adjust thepropeller in a pitch lining direction, hydraulic liuid from the coarsepitch side of the motor exhausting through the conduit means 5d, andwhen hydraulic fluid under pressure is supplied through the conduitmeans 5d the pitch change motor is operated to `adjust the propeller inthe pitch coarsening direction, hydraulic iiuid from the line` pitchside of the pitch change motor exhausting through the conduit means 48.

As more fully described in Patent No. 2,934,153 there is also providedstop means for limiting ning of the pitch of the propeller. GURE 5 ofthe present drawings shows diagrammatically those features of thearrangement described in Patent No. 2,934,15 3 necessary to an under-Patented Mar'. i3, 1962 standing of the present invention. Mountedwithin the hub 1E, are axially-extending spring ngers 19 having stops 25at their free ends. The radially-inner faces of stops 25 rest on annularsurfaces 21a, 2lb or 210 of an axially movable slecve 2.1 according tothe axial position of the sleeve. The piston 15 has an annular extension26 formed with an internal shoulder 27. When stops 25 rest on surface21a, movement of piston 15 in the ining direction is limited by abutmentof the end surface of its annular extension 26 on stops 25 to providerst stop means; when the stops rest on surface 2lb, the end surface ofthe extension 26 passes `over stops 25, but as the piston l5 moves lalittle lfurther in the lining direction, the internal shoulder 27 comesinto abutment with stops 25 to provide second stop means. When the axialposition of sleeve 21 is such that the stops 25 rest against surface21C, the stops are completely removed from the path of the pistonextension 26 and offer no impediment to the travel of the pitch-changepiston 15.

The sleeve 21 is biased into the position shown by a spring 28 seatedagainst a part of the hub 11. To cause the `sleeve 21 to move so thatthe stops 25 spring into contact with surface 2lb, the pressure of fluidin the line pitch fluid conduit means i8 is allowed to rise above itsnormal operating maximum value. This causes a valve member 29 to beforced back against the pressure of its spring 30 and permits thepressure of fluid in conduit 48 to be applied to an annular' piston 31through conduit 32. The other end of piston 31 abuts sleeve 21 and thetravel of piston 31 under the fluid pressure is such as to move thesleeve 21 against its spring 28 only a sufficient distance to cause thestops 25 to engage surface 2lb. This arrangement thus constitutes rststop Withdrawal means.

To cause the sleeve 21 to move so that the stops 25 engage surface 21C,hydraulic fluid under pressure is supplied through conduit 55, annulus33 and ports 33a to move a piston 34 mounted in a cylinder 35 in the hub11 to the left in the drawing. The piston 34 has an extension 34a withan outaturned flange 36 which engages round an in-turned flange 37 `onsleeve 21, so that sleeve 21 is carried to the left in the drawings withpiston 34 a sufricient distance to bring surface 21e into contact withthe stops 25, This arrangement thus constitutes second stop withdrawalmeans.

The conduit means 55 is separate from, that is to say has nocommunication with, the tine and coarse pitch uid conduit means 48 and58, and is generally referred to as the third oil line.

The cylinder space beyond annular piston 31 is vented through port 39and an annular recess 40 to a drain duct 41. The space beyond the valvemember 29 is also vented to drain duct 41.

The propeller, according to the present invention, as so far described,may be constructed as described in the specification and shown in thedrawings of co-pending United States ypatent application Serial No.671,783 tiled July l5, 1957, now Patent No. 2,934,153.

For the purpose of the present example now being described, however, itis lassumed that said first said stop withdrawal means is operative torender the iirst stop means inoperative and the said second said stopmeans is operable to render said second stop means inoperative as in`the case of the propeller described in the speciiication and shown inthe drawings of application Serial No. 671,783 -now Patent No.2,934,153.

The electro-hydraulic control system of the propeller now beingdescribed is located outside the propeller hub and is not rotatable withthe hub. The control system comprises a fine pitch fluid conduit. 48', acoarse pitch iiuid conduit 50', and a third oil line 55 whichcommunicate respectively through the transfer muti X-X with the conduitmeans 48, 50 and 55 previously described.

The control system further comprises a constant speed unit, generallyindicated at 67. The unit comprises a spool valve 68 having lands 69 and711, the valve 68 being slidably housed in the casing of the unit. Theunit further comprises in Well known manner flyweights 72 pivotallymounted as at 73 and arranged for rotation about the longitudinal axisof the spool valve 615.

The yweights bear against the underside of flange 68a on the spool valveand control the position of the spool valve, also in well known manner,to maintain the speed of the propeller constant at a speed determined bythe load in a Speeder spring 74, by adjusting the pitch of thepropeller.

The Speeder spring is engaged between the flange 68a and an inwardlydirected flange at the lower end of a rack sleeve 76 slidable in theupper part of the constant speed unit casing to adjust the loading inthe speeder spring 74, a pinion 77 being provided to co-operate with therack teeth and adjust the position of the sleeve 76 in the constantspeed unit housing, the pinion having a lever 77a movable through asuitable control range to adjust the datum setting of the constant speedunit.

The spool valve extends upwardly through the sleeve 76 and is formed atits upper end with a head 82C. A forked lever 84, pivoted to theconstant speed unit casing, is provided, this lever when moved in theanticlockwise direction in the drawing engaging beneath the head 82C tolift the spool valve 68 to supply hydraulic fluid under pressure throughthe coarse pitch fluid conduit '50 when it is required to feather thepropeller. The forked lever 84, and its associated control linkage (notshown), forms a manual feathering control for the propeller.

A piston 318 slidable in a cylinder 329 formed in the upper part of theconstant speed unit casing above the head 82C of the spool valve 68 hasa piston rod 332 connected with lost motion, as at 319, to the head 52e,the arrangement being such that the head 82e has suicient freedom ofmovement within the part 319 of the piston rod 332 to allow the spoolvalve 68 to perform its normal control movements under the action of theflyweights 72, when the piston 318 is in its lowermost position as shownin the drawing. A spring 330 is provided urging the piston 31S t-ovthisposition, and the cylinder space above the piston 318 is communicatedthrough a conduit 314 with the upper part 97 of the constant speed unitcasing which houses the flyweights 72. The piston 313 is displaceableupwardly in the drawing byrhydraulic fluid under pressure suppliedthrough conduit 326 and to port 327 in the constant speed unit casing tooverride the flyweights 72 and displace the spool valve 68 upwardly forthe purpose here inafter described.

The constant speed unit has a pump S6 which receives hydraulic fluidthrough a conduit 87, the conduit 37 communicatin'g with the lubricatingsystem of the engine which is employed to drive the propeller. Thislubricating system is usually maintained at a pressure of about 70 lbs.per square inch, The pump 36 is arranged to be driven by the enginewhich drives the propeller in well known manner, and delivers lluidunder pressure through a conduit 89 to a port 9i) in the constant speedunit housing7 port 911 opening between the lands 69 and 70 of the Yspool valve 68.

The ne and coarse pitch fluid conduits 43 and 5d' communicate with theinterior of the constant speed unit housing through ports 93 and 92respectively, and, in the equilibrium position of the spool valve 68,that is to say, when the propeller is in an on-speed condition, thelands 69 and 7 (l close off the ports 92 and 93 respectively `from theannular space 91 between the lands, which space is at all times incommunication through the port 9G and the conduit S9 with the deliveryside of the pump 86.

A chamber 94 in the constant speed unit housing below the valve '68communicates through a conduit 95 with the suction side of the pump 86,and through a bore 96 in the valve 68, with the upper part 97 of theconstant speed unit housing.

When the propeller overspeeds, the yweights 72 move outwardly and liftthe spool valve 68 thereby placing the coarse pitch Huid conduit 50 incommunication with the space 91 and the tine pitch conduit 48 incommunication with the chamber 94. Hydraulic fluid under pressure thenflows `from the space 91 through the port 92, the conduit 50', thetransfer muti X-X and the conduit means 5t? to the coarse pitch side ofthe pitch change motor to adjust the propeller in the pitch coarseningdirection, hydraulic duid from the fine pitch side of the pitch changemotor exhausting through the conduit means 4S, the transfer muff X--X,the conduit 48', port 93, chamber 94, and the duct to the suction sideof the pump S6. In a similar way when the propeller underspeeds, theflyweights 72 move inwardly thus allowing the valve 68 to be loweredunder the action of the spring 74 and hydraulic uid under pressurepasses from the space "91 into the ne pitch conduit 48' and thus to thetine pitch side of the pitch change motor to adjust the propellertowards fine pitch, hydraulic fluid on the coarse pitch side of thepitch change motor exhausting through the conduit means 5d, the muffX--X, the conduit 50", the port 92, the space 97, the bore 96, thechamber '94 and the duct 95 to the suction side of the pump 86.

The pump 86 delivers to the space91 through a nonreturn valve 80 and arelief valve 83 is connected between the suction side of the pump 86 andthe delivery side of the pump 86 upstream of the non-return valve 80.

In addition to the constant speed unit pump 86 there is also provided afeathering pump 79 which is used to feather and unfeather the propeller,the pump delivering through a conduit 78 and a non-return valve 85 tothe conduit 89 downstream of the non-return valve 80. A relief valve 81is provided for the feathering pump connected between the suction anddelivery sides of the pump. The feathering pump is usually driven by anelectric motor set in operation when it is required to feather andunfeather the propeller.

A conduit 10d leads from the conduit39, downstream of the non-returnvalve 811, to a port 150 in the valve housing 11M of a valve meansgenerally indicated at 103 and a conduit 151 leads from a port 152 inthe housing 104 to a first valve port 153 in a valve chamber 154 of anelectrohydraulic valve means generally indicated at 1111. The valvemeans 1111 comprises an electric solenoid 161:1 and a second valve port155 which communicates the valve chamber 154 through a conduit 118 witha drain channel 119 the pressure in which is maintained at 5 lbs. persquare inch by a non-return valve 120.

The valve means 101 also comprises a valve member 101k which isdisplaceable against the action of a spring 156, when the solenoid 161:1is energised, to open the valve port 153 and close the valve port 155,the valve member 101!) being returned by the spring 156 to its positionas shown in the drawing when the solenoid 16M is de-energised, that isto say, a position in which it closes the valve port 153 and opens thevalve port 155.

A conduit 1,1@ communicates with the valve chamber 154 through a thirdport 157 and leads to a port 158 in the valve housing 1de. A furtherport 159 in the valve housing 11E-dopens to a conduit 112 whichcommunicates with the cylinder 1d@ of a piston and cylinder assembly,generally indicated at 161, on the right hand side of the piston 11d ofthe assembly in the drawing.

The cylinder 16d, on the left hand side of the piston 114 in thedrawing, houses a tine pitch pressure conduit relief valve 115. Therelief valve has a spring 162 urging the valve on to a seating to closea port 163 communi cated, through a conduit 138, with the `fine pitchconduit t', the spring 162 engaging between the valve 115 and the piston114.

The relief valve is arranged to open the ne pitch fluid conduit d3 tothe coarse pitch uid conduit 511 when .5 the pressure in the conduit 48rises abdve the normal operating maximum value. To this end the cylinder160 to the left of the piston 114 in the drawing is communicated througha conduit 137 with the conduit 50'.

During normal operation the piston 114 is maintained in its position asshown in the drawing by the spring 162 and the coarse pitch uidpressure. When the piston 114 is displaced to the left in the drawing,however, by hydraulic fluid under pressure supplied through the conduit112, the piston compresses the spring 162 and engages the valve 115 toload the valve, thereby permitting the pressure in the line pitch fluidconduit 48 to be increased above its normal operating maximum value, toa value determined by the setting of the relief valve 88.

The valve means 101 has a further port 165 communicating the valvechamber 154 with a conduit 116 which leads to a valve port 167 of asecond electro-hydraulic valve means generally indicated at 117, Thevalve means 117 has the construction previously described for the valvemeans 101. Thus the valve port 167 opens into a valve chamber 168 whichcommunicates through a further valve port 169 with the drain conduit119. A valve member 117b is maintained in its position as shown in thedrawing, by a spring 170, when a solenoid 11711 of the Valve means 117is de-energised. In this position the valve member 117b closes the valveport 167 but is displaced from the valve port 169, the chamber 168therefore being communicated with the drain channel 119. When thesolenoid 117e is energised, however, the valve member 117 b is displacedagainst the action of the spring 170 to open the port 167 and close theport 169.

A conduit 122 communicates the valve chamber 168, through a port 171,with a hydraulic relay generally indicated at 172, which relay isoperable by hydraulic fluid under pressure to displace a hydraulicvalve, generally indicated at 127 from a closed position to an openposition.

The hydraulic relay 172 and the hydraulic valve 127 are housed in acommon housing 123 and the relay is in the form of a piston and cylinderassembly, the piston 124 of which is connected to operate the valve 127.The valve 127 comprises a pair of conical valve members mounted on a rodconnected to the piston 124, and the rod passes through a bore part 173in the housing 172, the valve members being arranged one on each side ofthe bore part 173. l

In the drawing the hydraulic valve 127 is shown in its closed positionin which the piston 124 is held displaced to the left in the drawing bya spring 174. In this position the hydraulic valve 127 closes the borepart 173 to a chamber 126 in the right hand end, in the drawing, of thehousing 123 and opens the bore part 173 to the cylinder 176 of the relayon the right hand side of the piston 124 in the drawing. The chamber 126communicates through a conduit 125 with the conduit 89 downstream of thenonreturn valve 80 and the third oil line 55 opens through the housing123 into the bore part 173.

When hydraulic fluid under pressure is supplied through the conduit 122the piston 124 is displaced to the right in the drawing and the valve127 is moved to its open position, hydraulic fluid under pressurepassing from the conduit 89 through the conduit 125 into the chamber 126through the bore part 173 into the third oil line 55.

When the valve 127 is in its closed position the third oil line 55 iscommunicated through the bore part 173 with the cylinder space on theright hand side of the piston 124 and through a conduit 129 with adrain, the conduit 129 including a non-return valve 130 set to a drainpressure of 25 lbs. per square inch.

A further conduit 131 communicates the conduit 95 with the cylinder 176on the right hand side of the piston 124 in the drawing, the conduit 131containing a restriction 132 designed to pass a small amount ofhydraulic fluid, for example, one hundred pints per hour. The purpose ofthe conduit 131 is hereinafter described.

A branch conduit 321 is taken from the conduit 100 to a valve port 322of an auto coarsening electrohydraulic valve means generally indicatedat 320. The valve means 320 has the construction previously describedfor the valve means 101. Thus the valve port 322 opens into a valvechamber 350 which communicates through a further valve port 324 with aconduit 325 which in turn communicates with the drain channel 119. Avalve member 320b is maintained in its position as shown in the drawing,by a spring 323, when the solenoid 320a of the valve means 320 isde-energised. 1n this position, the valve member 32011 closes the valveport 322, but is displaced from the valve port 324, the chamber 350therefore being in communication with the drain channel 119. When thesolenoid 320er is energised, however, the valve member 320I; isdisplaced against the action of the spring 323 to open the port 322 andclose the port 324. The conduit 326 previously described opens into thevalve chamber Referring now again to the valve means 103, the housing104 of this valve means has a further port 180 which opens to a by-passconduit 113 which communicates with the conduit 112. A still furtherport 181 in the housing 104 opens to a conduit 121 which communicateswith the drain channel 119.

The valve means 103 comprises a spool valve 182 having a central bore183 which communicates a space 184 in the housing 104, below the valvemember 182 in the drawing, with a space 185 in the housing 104, abovethe valve member 1-82 in the drawing, and a conduit 109 communicates thespace 184 with the space 97 in the constant speed unit casing.

The valve member 182 has three lands 105, 106 and 107 spaced apart anddefining two annular spaces 102 and 111 in the housing 104.

Within the housing 104, and in the space 184, is pivotally mounted cammeans generally indicated at 108 (see FIGURE 7). The cam 108 engages theValve member 182 and is manually operable in one direction to displacethe valve member 182 from an intermediate position in which it is shownin the drawing, upwardly in the drawing, when the feathering control ofthe propeller is actuated, and from its intermediate position,downwardly in the drawing, when a further manual control is operated.

In the present example this further manual control is constituted by thefeathering control, the lever 84 of which has a range of movement in theclockwise direction in the drawing other than to effect feathering ofthe propeller, the lever 84 when moved in the clockwise direction in thedrawing, adjusting the cam means 108 to move the valve member 182downwardly.

In the intermediate position of the valve member 182 the annular space111 communicates the ports 158 and 159 and the annular space 102communicates the ports and 152. Furthermore, when the valve member 182is in its intermediate position, the land 106 closes port 181 and theland 105 closes the port 180.

When the valve member 182 is displaced upwardly in the drawing, that isto say when the feathering control is operated to feather the propeller,the land 105 closes the port 150. Furthermore, the port 152 iscommunicated with the port 181 through the annular space 102.

When the valve member 182 is displaced downwardly in the drawing, land107 closes the port 153 and land 106 closes the port 152. Furthermore,the port 150l is placed in communication with the port 180 through theannular space 102.

During normal operation of the propeller, with the propeller constantspeeding under the control of the constant speed unit in a pitch changerange limited in the pitch ning sense by the rst pitch stop previouslydescribed, the valve member 182 is maintained in its intermediateposition as shown in the drawing and the solenoids 101a and 117e of thevalve means 101 and 117 remain deenergsed. Under these conditions thecylinder on the vright hand side in the drawing of the piston 114 iscommunicated through the conduit 112, the port 159, the annular space111, the port 15S, the conduit 1111, the port 157, the val-ve chamber154, the port 155, the conduit 118 and the drain channel 119 with adrain, and the piston 114 remains displaced to the right in the drawingas shown, the relief valve 115 being therefore free to relieve thepressure in the ne pitch fluid conduit 43 if the pressure in the iinepitchuid conduit should rise above its normal operating maximum value.

Furthermore, the cylinder 176 y011 the left hand side of the piston 124is communicated also with the drain channel 119 through the port 271,the conduit 122, the port 171, the valve chamber 168 in the valve means117, and the port 169. r Consequently the piston 124 remains displacedto the left in the drawing under the action of the spring 174, and thehydraulic valve 127 is maintained in its inoperative position.l

When it is required toA operate the first stop withdrawal means in orderto render the rst stop means inoperative so that the propeller may beadjusted into a pitch which is less than said first predetermined pitchbut greater than said second predetermined pitch, the solenoid 101:1 ofthe valve means 101 is energised.

Energisation of the solenoid 101a d isplaces the valve member 101b toopen the valve port 153 and close the valve port 155 as previouslydescribed. Hydraulic fluid under pressure then passes from the pump 86through the conduit`89`and the nonreturn valve 80 to the conduit 100,and through the conduit 100 to the port 150, and then through theannularspace 102, the port 152, the conduit 151, the port 153, the valvechamber 154, the port 157,

the conduit 110, the port 158, the annular space 111, the port 159 andthe conduit 112 to the cylinder 160 on the right hand side of the piston114, and the piston 114 isconsequently displaced to the left in thedrawing to load the relief valve 115 as previously described, hydraulicuid exhausting from' the cylinder 160` on the left hand side of thepiston `114 through the conduit 137 in the vcoarse pitch fluid conduit50', which under the condi- With'thesuction side of the pump 86.

' It should perhaps here be explained that when it is required to renderthe rst stop means inoperative, the

ydatum of the constant speed unit is adjusted to call for a propellerpitch less than that determined by the first stop means. In consequenceof this the propeller fines off on to the first'stop means and theconstant speed unit maintains the fine pitch uid conduit 48 incommunication with the delivery side of the pump 86. As soon as therelief valve 11S is gagged therefore the pressure of fluid in the finepitch uid conduit is allowed to build up above its normal operatingmaximum value and the first stop withdrawal means is operated torender'the first stop means inoperative so that the propeller is able tone olf to the pitch called for by the constant speed unit.

The solenoid ltla of the valve means 101 is maintained in its energisedstate whilst the propeller is operating at a pitch less than said iirstpredetermined pitch. When it is required to render the second stop meansinoperative in order to adjust the propeller into a pitch less than saidsecond predetermined pitch, the solenoid 117a of the valve means 117 isenergised whereupon hydraulic fluid under pressure passes from the pump86 through conduit 39 and the non-return valve St) to the conduit 100and through the port 150, the annular space 102, the port 152, theconduit 151, the port 153, the valve chamber 154, the port 165, theconduit 116, the port 167, the valve chamber 16S, the conduit 122 andthe port 271, to the left hand side in the drawing of the piston 124 andthe piston 124 is displaced to the right in the drawing to communicatethe third oil line 55 through the bore part 173, the vchamber 126 andthe conduit 125 with the conduit 89 so that hydraulic fluid underpressure passes from the pump `86 into the third oil line 55' to operatethe second stop withdrawal means to render the second stop meansinoperative.

in the present example the second stop means is a Hight tine pitch stopwhich is required to be maintained operative during all phases offlight, and removed only after touch down in order that the propellermay be adjusted into a superiine pitch to provide windmill braking onthe runway.

To achieve this end a pilots supertining master lever 201? is provided(see FGURE 3) which when moved to superfine selecting position isarranged to close a switch 2111 to energise the solenoid coil 117a.

lf, during operation of the propeller, it is required to feather thepropeller, the manual feathering control is operated to lift theconstant speed unit valve 63 to: supply hydraulic uid under pressure tothe coarse pitchz uid conduit 511'` and to place the tine pitch fluidconduit 48 in communication with the suction side of the con-- stantspeed-unit pump. The feathering pump motor 79 is also started to supplyhydraulic fluid under pressure to the constant speed unit.

Operation of the manual feathering control actuatesI the cam means 103to lift the valve member 182 so that the land 1115 closes the port 151i,and opens the port 152 to the port 181. Shouid the piston 114 be loadingthe relief valve 115 when the feathering control-is operated, therefore,the spring 162 returns the piston 114 to its position as shown in thedrawing, hydraulic fluid exhausting from the right hand side of thepiston through the conduit 112, the port 159, the annular space 111, theport 158, the conduit 1111, the port 157, the valve chamber 154, thevalve port 153, the conduit 151, the port 152, the annular space 162,the port 181, and the conduit 121 to the drain channel 119. The land 166and the port 181 therefore constitute a valve means operativelyconnected with the feathering control and operable when the featheringcontrol'is operated to connect the cylinder with the drain channel 119.

1f, due to some failure of the valve means 101, it transpires that thevalve means becomes ineffective to initiate gagging of the relief valve115 in order to operate the first stop withdrawal means, the cam means1618 may be manually operated to lower the valve member 182 aspreviously described. Hydraulic fluid under pressure then passes fromthe pump 36 through the non-return valve titi into the conduit 11i@ andthrough the port 150, the annular space 1112, the port 18u, the by-passconduit 113 and the conduit 112 directly to the right hand side in thedrawing of the piston 114 to displace the piston and thereby gag therelief valve. 1t will be seen, therefore, that the land 1115 and theport 189 constitute a by-pass valve controlling the by-pass of hydraulicfluid under pressure from the conduit 19t? direct to the by-pass conduit113. When the valve member 152 is lowered this byepass valve is openedand when the valve member 182 is returned to its intermediate positionthis by-pass valve is closed. When the valve member 132 is lowered-theland 1117 closes the port 15S. The land 107 therefore constitutes ashut-off valve for closing the conduit 112 from communication with theconduit 11d, thereby preventing hydraulic iluid from passing from theconduit 101i through the by-pass conduit 113 and the conduit 112 to thevalve chamber 154 and from the valve chamber through the port 15S to thedrain channel 119.

The function of the auto coarsening valve means 321i is generally asdescribed in the specification of United States patent applicationSerial No. 479,576 led Jaunary 3, 1955, now Patent No. 2,944,769 in thename of T. E. Godden and E. H. Morris and assigned to instant assignee.

The auto coarsening valve means is automatically energised in the eventthat due to some mechanical failure the propeller pitch unintentionallydrifts below the pitch set by the flight line pitch stop, in the presentexample 22.

Referring to FlGURE 3, the solenoid coil 320g of the valve means 320 isconnected in series with a relay operated switch 204, and a propellerhub switch 400, across a current source 401, 102. The relay operatedswitch 204 is normally closed and the hub switch 400 is normally open.The hub switch is however closed and held closed by the propeller whenthe propeller blades tine oi below a pitch angle slightly less than thatset by the flight line pitch stop, in the present example 20. In thesecircumstances the solenoid coil 320a is energised and the valve member320b is displayed downwardly against the action of the spring 323 toopen the valve port 322 and close the valve port 324. Hydraulic fluidunder pressure then passes from the delivery side of the constant speedunit pump, through the conduit 100, the conduit 321, the valve chamber350 and the conduit 326 to the cylinder 329 on the lower side of thepiston 31S, and the piston 318 is displaced upwardly, against the actionof the spring 330 thereby taking up the lost motion at 319 and liftingthe spool valve 68 to select increased pitch. A temporary coarsening ofthe pitch of the propeller blades is thereby eifected, the lining otmovement being checked and the pitch being coarsened to a pitch greaterthan 20. As soon as the pitch is increased beyond the 20 pitch angle thehub switch 400 opens and the valve means 320 is de-energised so that thevalve member 320b returns to its position as shown in the drawingcommunicating the cylinder 329 on the lower side of the piston 310 withthe drain channel 119 so that the spring 330 is able to return thepiston 318 to its lowermost position thereby replacing the spool valve68 under the control of the fiyweight 72.

If then the propeller still tends to line oi the above describedsequence of operation is repeated, the propeller pitch being repeatedlycoarsened each time the blades tine off below a 20 pitch angle, so as tomaintain the propeller blades at a mean pitch angle greater than 20,until such time as a corrective action is taken by the pilot. To thisend a warning light 320e may be incorporated in the electrical circuitassociated with the solenoid coil 32011 so that the pilot will be warnedthat the auto coarsening Valve means is operating and can take thenecessary action to prevent the propeller pitch ning off below the pitchnormally set by the flight tine pitch stop.

lt will be appreciated that when it is required to adjust the pitch ofthe propeller into the superne pitch change range below the flight nepitch stop it is necessary to render the auto coarsening meansinoperative.

Adjustment of the pitch into the superne pitch change range is requiredonly after touch down of the aircraft as previously stated, and in thesecircumstances the engine driving the propeller will be throttled back toa predetermined low throttle setting as previously explained to allowmovement of the master lever 200 previously described to its position inwhich it initiates the withdrawal of the flight fine pitch stop.Movement of the master lever 200 to initiate the withdrawal of the Hightfine pitch stop closes the switch 201, and closure of the switch 201 isarranged to energise a relay 203 to open the switch 204, and so isolatethe solenoid coil 320a and render the auto coarsening means inoperative.

in order to lubricate the transfer muff X-X, pipe means is providedleading hydraulic uid, which is also lubricating fluid, from the thirdoil line 55' to points of usage in the muil?. When the hydraulic valve127 is in its inoperative position as shown in the drawing, hydrauliciuid is supplied into the third oil line in sufficient quantities forlubricating the mut trom the suction side of the pump 36 through theconduit 131 into the cylinder 176 on the right hand side of the piston12d and through the bore part 173 into the third oil line.

With the electro-hydraulic control system described with reference toFIGURE l, it will be seen that if a failure of the solenoid valve means101 occurs such that it becomes impossible to energise the solenoid ofthe valve means or to displace the valve member 1011i of the valve meansdownwardly by energising the solenoid of the valve means, there is nosource of hydraulic fluid under pressure available at the valve `means117 for operating the hydraulic relay 172. This is because hydraulicfluid under pressure passes to the relay 172 via the valve chamber 15dof the valve means 101 which chamber is communicated with the pressuresource only when the valve member 1011) is displaced downwardly.

Upon failure of the valve means 101 therefore although it is possible towithdraw the cruise stop by manual adjustment of the valve 103 noalternative means is available for lwithdrawing the night ne pitch stop.This may prove objectionable in certain circumstances,l and in ordertherefore to overcome this diiculty the system described may be modifiedby connecting the conduit 116 with the conduit 112, as shown in chaindotted lines in FIGURE l, instead of with the valve chamber 154, theport in this case being blanked off.

With this arrangement, following a failure of the valve means 101, andmovement of the valve 103 downwardly to withdraw the cruise stop,hydraulic fluid under pressure is available from the conduit 112 4foroperating the hydraulic relay 172 when the valve means 117 is energisedto withdraw the Hight fine pitch stop. Furthermore, since the conduit112 communicates with the valve chamber 154 through the valve 103 whenthe valve is in its intermediate position as shown in FIGURE l,hydraulic fluid under pressure is available in the conduit 112 foryoperating the relay 172 when the valve means 117 is energised afteroperation of the valve means 101 to withdraw the cruise stop.

The propeller described with reference to FIGURES l and 5 may bemodified as shown in FIGURE 6 to function as a reversible pitchpropeller. In this case the propeller is provided in addition with athird stop means comprising another internal shoulder 38 on the pistonextension 26 acting in conjunction with stops `25 and operable toprevent relative movement of the ram 15 and cylinder 16 of the pitchchange motor of the propeller to adjust the propeller into reversepitch.

The propeller has rst and second stop means as previously described, andthe piston 31 is operable to render the first stop means inoperative.The second stop withdrawal means comprising the piston 34 is however, inthis case operable to render both the second and third stop meansinoperative. When it is required to render the second stop means, thatis to say, the night pitch stop, inoperative, hydraulic uid underpressure is supplied through the third oil line 55 to operate the piston34 to render both the second and third stop means inoperative. As soonas the propeller has lined oit below the second stop means the third oilline 55 is communicated with drain through the hydraulic relay 172. Whenthe valve element of this relay is positioned such that no Huid pressureis introduced into the third oil line, then the third oil line iscommunicated with drain through the relay, the conduit 129 and thenon-return valve 130, the latter being set to drain pressure of 25pounds per square inch. The third stop means is thereby -re-set to limitpitch change at a pitch angle of 0.

When it is required to adjust the propeller into reverse pitch,hydraulic iluid under pressure is again supplied through the third oilline 55 to operate the piston 34 to render the third stop meansinoperative so that the propeller can be adjusted into reverse pitch.

The electro-hydraulic control system of the propeller is modified asillustrated in FIGURE 2, and these modifications, and the manner ofoperation Lof the modified control system, will now be described indetail.

Referring to FIGURE 2, the upper part of the constant `speed unit casingis in this case formed with a further cylinder 313 above the `cylinder329, and the cylinder 313 y houses a piston 311 having a piston rod 315which is slidable in a bore 316` in a partition 317 between thecylinders 3173 and 329, the piston rod 315'extending downwardly throughthe piston rod 332, which in this case is hollow, towards the` head 82eof the spool valve 63, a space being left between the end of the rod`315 and the head 82C rsuicient to allow for normal control movements ofthe valve 68 under the control of the yweights 72 when the piston 311 isin its position as shown in the drawing.

A spring 312 is engaged between the piston 311 and the partition 317,urging the piston 311 to this position. Y A port 331 is formed in thepartition 317, and the conduit `314 in this case communicates with thecylinder 313 below the piston 311 through a port 313e.

A conduit 302 is taken from a port 301 in the valve i chamber 168 of thevalve means 117 to a valve port 303 of ,a reversing electro-'hydraulicvalve means, generally v indicated at 304. The Valve means 304 has theconstruction previously described for the valve means 101. Thus, thevalve port 303 opens into a valve chamber 380 which communicates througha further valve port 306 with a conduit 307 which communicates with thedrain channel 4119. A valve member 304b is maintained in its position asshown in the drawing by a spring 305 when the solenoid 304a of the valvemeans 304 is de-energised. In

v this position the valve member 304i: closes the valve port 303, but isdisplaced from the valve port 306, the chamber 3S0being therefore incommunication with the drain channel '119. When the solenoid 304e isenergised however, the valve member 304b is displaced against the actionof the spring 305 to open the port 303 and close the The valve chamber380 has a port 300 communicated, by means of a conduit 309 with thecylinder 313 above the piston 311.

The remainder of the hydraulic control system is as previously describedwith referencel tot FIGURE l, and

the conduit 116 may be connected either with the port ter ylever ismoved to its superline .selecting position, a

switch 209 which is associated with the throttle lever of the enginedriving the propeller, which switch is held closed when the throttlelever is in a forward speed setting but which is opened when thethrottle lever is moved through a gate into a reverse speed range, andthe relay coil 207 of the relay operated switch 200.

A still further circuit is also provided across the current source 401and 402, this circuit including a switch 210, interconnected with thethrottle lever so as to be open when the throttle lever is in a forwardspeed setting and closed when the throttle lever is in a reverse speedsetting, and the solenoid coil 304m of the reversing valve K means.

When it is required to `adjust the propeller from a pitch greater tha-n22 but less than 37 into its superne pitch change range, the lever 200is moved to its position selecting superne pitch thereby closingswitches 201 and 202. In these circumstances the throttle lever will beat the predetermined low setting in its forward speed range, and inconsequence the switch 209 will be closed and the switch 210 will beopen. Closure of the switch 202 will therefore have no immediate effect,but closure of the switch 201 energizes the solenoid coil 117e and inView of this hydraulic liuid under pressure is supplied through theconduit 55 and the third -oil line 55 to manner previously described,but in this case to render both the flight fine pitch stop and thereverse pitch stop inoperative. The propeller is then free to tine olfinto the superiine pitch Kchange range. As soon as the pitch of thepropeller is reduced below 20 the hub switch 400 closes but since switch201 is closed, the autocoarsen ing coil 320e is isolated because therelay 203 will have opened the switch 204. Closure of the switch 400cannot therefore initiate the operation of the auto coarsening valvemeans 320. Closure of the switch 400, however, energises the relay coil207 through switch 202 and switch 209 both of which switches are closedin the circumstances being described, and consequently switch 208 isopened, thereby de-energising the solenoid coil 117a so that the thirdoil line 55 is communicated with drain, and the reverse pitch stop isreset.

When it is required to adjust the propeller from its superiine pitchchange range into reverse pitch, the throttle lever 403 is moved intoits reverse speed range thereby closing the switch 210 and opening theswitch 209. Opening of the switch 209 de-energizcs the relay 207 so theswitch 208 closes to energise the solenoid coil 117a and the second saidstop withdrawal means is again operated to render the reverse pitch stopinoperative.

Closure of the switch 210 energises the reversing solenoid coil 304e sothat the valve member '304b is displaced downwardly in the FIGURE 2 toopen the valve port 303 and close the valve port 306. Hydraulic liuidunder pressure then passes from the valve chamber 16S through the port301, conduit 302, valve port 303, valve chamber 330, port 30S, conduit309 to the cylinder '313 on the upper side of the piston 311 in thedrawing, and the piston 311 is moved downwardly against the action ofthe spring 312 so that the piston rod 315 engages the head 82e of thespool valve 68 and pushes the spool valve downwardly to a position inwhich it selects decreasepitch. Hydraulic fluid under pressure isconsequently supplied through the tine pitch liuid conduit 48 to theline pitch side of the pitch change motor to actuate the motor to adjustthe propeller into reverse pitch.

When it is required to adjust the propeller out of the reverse pitchrange into the superline pitch range, for example, `for taxiing on theground, the throttle lever is moved back into its forward speed range sothat switch 210 is opened and switch 209 is closed. Opening of switch210 de-energises the coily 304g with the result that the cylinder 313 iscommunicated with the drain channel 119 and the piston 311 is returnedby the spring 312 to its position shown in the drawing, so that thespool valve 68 again comes under the control of the flyweights 72.Closure of the switch 209 energises the relay coil 20'7 and opens theswitch 208 so that the solenoid coil 117a is deenergised and the thirdoil line communicated with the drain, thus allowing the reverse ptichstop to be re-set as soon as the propeller Iis adjusted into thesuperline pitch change range by the constant speed unit which will callfor positive pitch as soon as the throttle lever is moved into itsforward speed range.

When it is required to adjust the propeller from its superiine pitchchange range into a pitch greater than 22, for example, when preparing`for take-oli, the lever 200 is moved back from its superne selectingposition thereby opening the switches 201 and 202. Opening of switch 202de-energises the relay coil 207 allowing switch 208 to close. Thesolenoid coil 1170v is not, however, energised, because switch 201 hasbeen opened.

Opening of switch 201 de-energises the relay coil 203 so that switch 204closes and energises the solenoid coil 320d with the result that thelyweights 72 are overridden and the spool valve 68 moved to ytheincrease pitch position by the piston 318.

Movement of the lever V200 releases the throttle lever for movement intoa higher throttle setting, and as the propeller pitch increases above20, hub switch 400 opens, thus -de-energising the solenoid coil 320a andreturning the spool valve 60 to the control or" the iiyweights 13 72,which in view of the increasing propeller speed, continue to call forincreased pitch, until tinally the pitch attains a value greater than22, whereafter the fine pitch stop is automatically re-set. Resetting ofthe flight cruise stop also takes place automatically as soon as thepitch of the propeller is increased beyond 37.

With any of the control systems described, it will be seen that the autocoarsening valve means 320 is supplied with hydraulic uid under pressurethrough the conduit 321 direct from the conduit 100 which communicatesdirectly with the delivery side of the pump S6. The valve means 32%) istherefore hydraulically independent of the valve means 101, 117 and, inthe case of the reversible pitch construction the valve means 3114 isable to function to prevent the propeller inadvertently fining off belowa pitch angle of even although some failure of the otherelectro-hydraulic valve means or their electric control circuits occur.

For example, when the propeller is at a pitch above the flight finepitch stopbut below that set by the ight cruise stop, as would be thecase when the aircraft is preparing to land, any failure of the valvemeans 117 causing the flight fine pitch stop to be rendered inoperativecould, in the absence of the auto coarsening means, lead to danger inthat the propeller would be free to fine off into supertine pitch `andthereby bring about the onset of substantial windmilling drag possiblycausing the aircraft to yaw uncontrollably.

Under these circumstances however the auto coarsening valve means wouldbe able to function to limit the pitch lining movement at pitch angle of20.

When preparing to land with the Hight tine pitch stop for some reasoninoperative, particular danger could result but for the auto coarseningmeans if the reversing valve means in the case of the reversible pitchpropeller is inadvertently energised due to some electrical failure.Under these circumstances due to hydraulic fluid leakages, there may besufiicient hydraulic fluid passed to the cylinder 313 above the piston311 to move the piston 311 downwardly, the piston thereby adjusting thespool valve 68 to select decreased pitch. If this happens the propellerwould rapidly fine off to a pitch angle of 20 but further iining offmovement would be prevented by the auto coarsening means which,utilising the full delivery pressure of the pump 86, would be able toovercome the action of the piston 31.1 moved only by leakage pressure toadjust the spool valve 68 into a position selecting increase pitch, thehydraulic fluid in the cylinder 313 above the piston 311 exhausting tothe drain channel 119 through the valve chamber 16S and the valve port169.

lf the valve means 117 and the reversing valve means are, due tofailure, inadvertently energised the piston 311 would be displaceddownwardly by the full pump delivery pressure and there would be atrappped volume of hydraulic fluid in the cylinder 313 above the piston311 because the valve means .181 is energised. Under these circumstancesthe auto coarsening means would be unable to lift the spool valve 6% toselect increase pitch to prevent pitch fining below a pitch angle of 20and the only remedy would be for the pilot to `feather the propellerusing the manual feathering control lever S41. Movement of this lever tothe feather position releases any trapped volume of hydraulic Huid inthe cylinder 313 above the piston 311 in the manner hereinafterexplained in order that the spool valve 68 may be raised to selectincrease pitc Assuming now in the case of the reversible pitch propellerthat reverse pitch has been selected in the normal manner, that is tosay that all of the valve means 101, 117 and 3111i have been energisedand remain energised, but that some failure occurs which makes itnecessary immediately to feather the propeller. Under thesecircumstances, as in the case discussed above, it will be appreciatedthat there is a trapped volume of hydraulic fluid in the cylinder 313above the piston 311 preventing the spool valve 68 being lifted as isnecessary to feather the propeller.

When the lever 84 is moved to feather however the spool valve 182 islifted as previously described, so that the port 152 is communicatedthrough the annular space 102 with the port 131 and thus with the drainchannel 119. Lifting of the spool valve 182 therefore communicates thespace in the cylinder 313` above the piston 311 with the drain channel`119 through the conduit 309, the port 308, the valve chamber 380, thevalue port 303, the conduit 392, the port 301, the valve chamber 168,the valve port 167, the conduit 116, the port `165, the valve chamber154, the valve port 153, the conduit i151, the port 152, the annularspace 102, the port 181 and the conduit 121, thereby releasing thepiston 311 and allowing the spool valve 68 to be raised by thefeathering lever 84.

If the modied construction in which the conduit 116 is connected to theconduit 112 is adopted, raising of the spool valve 182 on fea-theringcommunicates the cylinder 313 above the piston 311 with the drainchannel through the conduit 112, the port 159, the annular space 111,the port 158, the conduit 1110, the port 157, the valve charnber 154 andso on as before.

If in the case of .the modified construction just referred to the spoolvalve 182 is in its lowered position just prior to feathering the valvemeans 101 having failed with the valve member 1Mb closing the valve port153, movement of the spool valve to its raised position on fea-theringcommunicates the cylinder 313 above the piston 311 with the drainchannel 119 through the port 157, the valve chamber 11'54, the port 155and the conduit 118.

With the modified construction as described with reference to FIGURE 1,used in conjunction with the further modications described withreference to 'FIGURE 2 in the case of the reversible construction, itwill be seen that upon failure of the valve means 101 and consequentmovement of the spool valve 182 downwardly to initiate operation of thefirst said stop withdrawal means, hydraulic fluid under pressure isagain available in the conduit 112 for operating the hydraulic relay 172when the valve means -117 is energised, and furthermore since thereversing valve means 304 is supplied with hydraulic fluid underpressure from the valve means 117, reversing may also be accomplished inthe normal manner. In the event that the valve means 101 is functioningin the normal manner, hydraulic uid under pressure is supplied to thevalve means 117 upon energisation of this valve means in the mannerpreviously described, and the reversing function is also still possible.

We claim:

1. A hydraulic variable pitch propeller having a hub, a plurality ofadjustable pitch propeller blades carried by the hub, and a pitch changemotor in the hub, said pitch change motor comprising a ram and cylinder,means operatively connecting the ram to the propeller blades, a pressuresource of hydraulic fluid under pressure, iine pitch fluid conduit meansbetween said pressure source and said motor for leading hydraulic uid toand `from the tine pitch side of said pitch change motor, a relief valvein communcation with said tine pitch iiuid conduit means, said reliefvalve being connected to said tine pitch fluid conduit means to relievethe pressure of iiuid in said ne pitch fluid conduit means when saidpressure exceeds a normal operating maximum value, a piston and cylinderassembly connected with said relief valve and operable to vary theloading on it, first auxiliary hydraulie fluid conduit means betweensaid pressure source and said cylinder of said assembly, firstelectro-hydraulic valve means in said rst fluid conduit means `andoperable to connect said pressure source and said cylinder of saidassembly to operate said piston and cylinder assembly, causing thelatter to load said relief valve, coarse pitch fluid conduit meansbetween said pressure source and said motor for leading hydraulic fluidto yand from the coarse pitch side of said 4pitchchange motor, iirststop annessa means in said motor operable to prevent relative movementof said `rarn and cylinder to adjust the propeller blades into a pitchless than a first predetermined pitch, second stop means in said motoroperable to prevent relative movement of said ram and cylinder to adjustthe propeller into a pitch less than a second predetermined pitch whichis itself less than said first predetermined pitch, first and secondhydraulically operable withdrawal means operatively connectedrespectively with the first land second stop means and each operable torender the Stop means connected thereto inoperative, a third linehydraulic fluid conduit means between said pressure Source `and saidsecond withdrawal means and separate of said fine pitch iiuid and coarsepitch fluid conduit means for leading hydraulic fluid to the secondwithdrawal means to operate said `second Withdrawal means, a hydraulicvalve in said third line c-onduit means, a hydraulic relay connectedwith said hydraulic valve to operate said hydraulic valve, secondauxiliary hydraulic fluid conduit means `between said pressure sourceand said relay, -asecond electro-hydraulic Valve means in said secondauxiliary conduit means operable to control the supply of hydraulicfiuid under pressure from said pressure source to said relay causing thelatter to operate said -hydraulic valve, third auxiliary conduitmeansbetween said fine pitch conduit means and said first withdrawal means,and valve means in said third auxiliary `conduit means and in connectionwith the nue pitch conduit means connected to operate when the pressureof fluid in said fine pitch iluid conduit means is increased above saidnormal operating maximum value to connect the supply of hydraulic fluidunder pressure in said fine pitch fluid conduit meanswith the firstwithdrawal means -to operate said first withdrawal means.

2. A khydraulic variable pitch propeller having a hub, a plurality ofadjustable pitch propeller blades carried by the hub, and a pitchchange-motor in the hub, said pitch change motor comprising a ram andcylinder, means operatively connecting the ram to the vpropeller blades,apressure source of hydraulic -iiuid under pressure, fine pitch fluidconduit means between said pressure source and said motor for leadinghydraulic fluid to and from the fine pitch side of said pitch changemotor, a relief valve in communication with said fine pitch fluidconduit means, said relief valve being connected to said tine pitchfluid conduit means to relieve the pressure of fluid in said fine pitchfluid conduit means when said pressure exceeds la normal operatingmaximum value, a piston and cylinder assembly connected with said reliefvalve and operable to vary the loading on it, first auxiliaiy hydraulictluid conduit means ybetween said pressure source and said cylinder ofsaid assembly, first electro-hydraulic valve means in said first fluidconduit means and operable to connect said pressure source and saidcylinder of said assembly to operate said piston and cylinder assembly,causing the latter to load said relief valve, coarse pitch fluid conduitmeans `between said pressure source and said motor for leading hydraulicfluid to and from the coarse pitch side of said pitch change motor,first stop means in said motor operable to prevent relative movement ofsaid ram and cylinder to adjust the propeller blades into a pitch lessthan a lirst predetermined pitch, second stop means in said motoroperable to prevent relative movement of said ram and cylinder to adjust`the propeller into a pitch less than a second predetermined pitch whichis itself less than said first predetermined pitch, first and secondhydraulically operable withdrawal means operatively connectedrespectively with the first and second stop means yand each operable torender the stop means connected thereto inoperative, a third linehydraulic -lluid conduit means between said pressure source Iand saidsecond withdrawal means and separate of said fine pitch fluid and coarsepitch fluid conduit means for leading hydraulic liuid to the secondwithdrawal means to operate said second withdrawal means,

a hydraulic valve in said third line conduit means, a hydraulic relayconnected with said hydraulic valve to operate said hydraulic valve,second auxiliary hydraulic fluid conduit means between said pressuresource and. said relay, a second electro-hydraulic valve means in saidsecond auxiliary conduit means operable to control the supply ofhydraulic fluid under pressure from said pressure source to said relaycausing the latter to operate said hydraulic valve, third auxiliaryconduit means between said fine pitch conduit means and said iirstwithdrawal means, and valve means in said third auxiliary conduit meansand inrconnection with the fine pitch conduit means connected to operatewhen the pressure of fluid in said line pitch fluid conduit means isincreased above said normal operating maximum value to connect thesupply of hydraulic fluid under pressure in said fine pitch fluidconduit means with the first withdrawal means to operate said firstwithdrawal means.

3. A propeller as claimed in claim 2 further having a drain conduit andrfirst duct means between said irst and second electro-hydraulic valvemeans wherein said rst electro-hydraulic valve means comprises anelectric solenoid energisable to actuate the valve means, a valvechamber, a first valve port in said valve chamber connected to the firstauxiliary conduit means from the source, a second valve port connectedto drain conduit, a third valve port connected to the first auxiliaryconduit means leading to the cylinder of the piston and cylinderassembly, a fourth valve port, said first duct means being connected tosaid fourth valve port, a valve member in said valve chamber, said valvemeans being movable from a lirst position in which it closes the firstvalve port to a second position in which it closes the second valveport, and spring means in operative connection with said member urgingsaid valve member into its said rst position, said solenoid, whenenergised urging said valve member against the action of the spring intothe second position, and wherein said second electro-hydraulic valvemeans comprises an electric solenoid energisable to actuate the valvemeans, a valve chamber, a first valve port connected to said first ductmeans which constitutes part of said second auxiliary conduit means, asecond valve port connected to the drain conduit, a third valve portconnected to said second auxiliary conduit means leading to said relay,a valve member in said valve cylinder, said valve means being movablefrom a rst position in which it closes the second valve port, and springmeans in operative connection with said valve member urging said valvemember into its said first position, said solenoid, when energisedurging said valve member against the action of the spring into thesecond position.

4. A propeller as claimed in claim 2 further comprising a constant speedunit having a hydraulic control valve in said fine pitch and coarsepitch conduit means, operable to connect either said fine pitch or saidcoarse pitch conduit means or neither to said pressure source,hydraulically operable coarsener overriding means movable into operativeconnection with said hydraulic control valve to adjust the latter toconnect said pressure source to said coarse pitch conduit means, fourthauxiliary hydraulic fluid conduit means connecting said coarseneroverriding means with said source, and third electro-hydraulic valvemeans in said fourth auxiliary conduit means operable to control theconnection of said coarsener overriding means with said source.

5. In an aircraft comprising a propeller-driving engine and means forvarying the speed of the engine in operative connection therewith, apropeller as claimed in claim 4 in operative connection with said motorto be driven thereby wherein the second and third electro-hydraulicvalve means each include a solenoid which when actuated operates itselectro-hydraulic valve means, said propeller first relay switch andoperable to open said switch, a propeller hub switch operativelyconnected to the said propeller blades and operated when said propellerblades fine off to an amount less than a predetermined amount, firstsuperning switch means operatively connected to the engine speed varyingmeans when said engine speed Varying means is within a predeterminedrange of movement, said first superfining switch means being moved bysaid engine speed varying means into a closed position when the enginespeed varying means is set to cause the engine speed to be below apredetermined value, a first line connection across said electricalsource and a second line connection across said electrical source andparallel with said first line connection, said second line connectionincorporating in series said propeller hub switch, said first relayswitch and the solenoid of said third electrohydraulic valve means andsaid first line connection incorporating the first switch solenoid, thesolenoid of second electro-hydraulic valve means in parallel with saidfirst switch solenoid, and said superfining switch means in series withboth solenoids.

6. In an aircraft comprising a propeller-driving engine and means forvarying the speed of the engine in operative connection therewith, apropeller as claimed in claim further comprising a second relay switchconnected in said first line connection, a second relay switch solenoidin operative connection with said second relay switch and operable toopen said second relay switch, a second superfiniug switch means to beclosed when said first superfining switch means is closed and to be openwhen said first superfining switch means is open, said second switchsolenoid and said second superfining switch means being connected inseries with one another in said second line connection, in parallel withsaid solenoid of the third electro-hydraulic valve means, and in serieswith said propeller hub switch.

7. A propeller as claimed in claim 2 further comprising a manuallyoperable first shut off valve in said first auxiliary conduit means,by-pass conduit means connected in said first auxiliary conduit means toby-pass said first electro-hydraulic valve means and a manually operableby-pass valve in said by-pass conduit means operable to connect saidcylinder of said piston and cylinder assembly to said pressure sourcewhile by-passing said shut-oil valve and said first electro-hydraulicvalve means.

8. A propeller as claimed in claim 7 wherein said manually operatedby-pass valve and said manually operated shut-off valve are operativelyconnected together so that when one of said manually operated valves isopen, the other is closed and Vice versa.

9. A propeller as claimed in claim 8 further comprising a secondmanually operated shut-off valve in said first auxiliary conduit meansoperable to cut off hydraulic fluid supply from the pressure source toboth the other said manually operated valves.

lO. A propeller as claimed in claim 9 further comprising a constantspeed unit having a valve in the coarse pitch conduit means and in thefine pitch conduit means and operable to connect said pressure source tosaid coarse pitch conduit means or said fine pitch conduit means orneither and a manually operated feathering control means in operativeconnection with said constant speed unit and with said second shut-offvalve and operable to override said constant speed unit to connect saidpressure source to said coarse pitch fluid conduit means andsimultaneously to shut off said second shut-off valve.

ll. A propeller as claimed in claim 2 wherein said firstelectro-hydraulic valve means is also connected in said second auxiliaryconduit means and is operable t0 connect said second electro-hydraulicvalve means to said pressure source.

12. A propeller as claimed in claim 2 comprising a drain conduit,wherein said first electro-hydraulic valve means comprises an electricsolenoid energisable to actuate the valve means, a valve chamber, afirst valve port in said valve chamber connected to the first auxiliaryconduit means from the source, a second valve port opening to saidchamber and connected to said drain conduit, a third valve port openingto said chamber and connected to the first auxiliary conduit meansleading to the cylinder of the piston and cylinder assembly, a valvemember in said valve chamber, said valve member being movable between afirst position in which it closes the first valve port and leaves thesecond valve port open and a second position in which it closes saidsecond valve port and opens said first valve port, and spring means inoperative connection with said valve member urging said valve memberinto its said first position, said solenoid, when energised urging saidvalve member against the action of the spring into the second position,wherein the second auxiliary conduit means communicates at its upstreamend with said first auxiliary conduit means at a point downstream ofsaid first valve port of the first electrohydraulic Valve means andwherein said second electrohydraulic valve means comprises an electricsolenoid er1- ergisable to actuate the valve means, a valve chamberhaving first, second and third valve ports opening thereto ywherein thefirst valve port is connected to said second auxiliary conduit meansleading to said first electro-hydraulic valve means, the second valveport is connected to the drain conduit, and the third valve port isconnected to said second auxiliary conduit means leading to said relay,a valve member in said valve chamber, said valve means being movablefrom a first position in which il closes the first valve port to asecond position in which it closes the second valve port, and springmeans in operative connection with said valve member urging said valvemember into its said first position, said solenoid, when energised,urging said valve member against the action of the spring into thesecond position.

13. A hydraulic variable pitch propeller having a hub, a plurality ofadjustable pitch propeller blades carried by the hub, and a pitch changemotor in the hub, said pitch change motor comprising a ram and cylinder,means operatively connecting the ram to the propeller blades, a pressuresource of hydraulic fluid under pressure, fine pitch fluid conduit meansbetween said pressure source and said motor for leading hydraulic fluidto and from the fine pitch side of said pitch change motor, a reliefvalve in communication with said fine pitch fluid conduit means, saidrelief valve being connected to said fine pitch fluid conduit means torelieve the pressure of fluid in said fine pitch fluid conduit meanswhen said pressure exceeds a normal operating maximum value, a pistonand cylinder assembly connected with said relief valve and operable tovary the loading on it, first auxiliary hydraulic fluid conduit meansbetween said pressure source and said cylinder of said assembly, firstelectro-hydraulic valve means in said first fluid conduit means andoperable to connect said pressure source and said cylinder of saidassembly to operate said piston and cylinder assembly, causing thelatter to load said relief valve, coarse pitch fluid conduit meansbetween said pressure source and said motor for leading hydraulic fluidto and from the coarse pitch side of said pitch change motor, first stopmeans in said motor operable to prevent relative movement of said ramand cylinder to adjust the propeller blades into a pitch less than afirst predetermined pitch, second stop means in said motor operable toprevent relative movement of said ram and cylinder to adjust thepropeller into a pitch less than a second predetermined pitch which isitself less than said first predetermined pitch, third stop means insaid motor operable to prevent relative movement of said ram andcylinder t0 adjust the propelier blades into a pitch less than a thirdpredetermined pitch, which is itself less than said second predeterminedpitch, first hydraulically operable withdrawal means operativelyconnected to said first stop means and operabl to render said first stopmeans inoperative, second hydraulically operable withdrawal meansoperatively connected to said second and third stop means and operableto render said second stop means inoperative when the propeller is in apitch setting between said first predetermined pitch and said secondpredetermined pitch and to render said third stop means inoperative whenthe propeller is in a pitch setting between said second predeterminedpitch and said third predetermined pitch, a third line hydraulic fluidconduit means between said pressure source and said second withdrawalmeans and separate of said fine pitch fluid and coarse pitch fluidconduitmeans for leading hydraulic fiuid to the second withdrawal meansto operate said second withdrawal means, a hydraulic valve in said thirdline conduit means, a hydraulic relay connected with said hydraulicvalve to operate said hydraulic valve, second auxiliary hydraulic fiuidconduit means between said pressure source and said relay, a secondelectro-hydraulic valve means in said second auxiliary conduit meansoperable to control the supply of hydraulic fluid under pressure fromsaid pressure source to said relay causing the latter to operate saidhydraulic valve, third auxiliary conduit means between said fine pitchconduit means and said first withdrawal means, and valve means in saidthird auxiliary conduit means and in connection with the fine pitchconduit means connected to operate when the pressure of fluid in saidfine pitch fluid conduit means is increased above said normal operatingmaximum value to yconnect the supply of hydraulic iiuid under pressurein said fine pitch fiuid conduit means with the first withdrawal `meansto operate said first withdrawal means.

14. A propeller as claimed in claim i3 further comprising a constantspeed unit having a hydraulic control valve in said fine pitch andcoarse pitch conduit means, operable to connect either said fine pitchor said coarse pitch conduit means or neither to said pressure source,hydraulically operable reversing overriding means movable into operativeconnection with said hydraulic control valve to adjust the latter toconnect said pressure source to said fine pitch conduit means,supplementary hydraulic fiuid conduit means between said pressure sourceand said reversing overriding means, fourth electrohydraulic valve meansin said supplementary conduit means operable to connect said pressuresource and said reversing overriding means.

l5. A propeller as claimed in claim 14 wherein said secondelectro-hydraulic valve means is also connected in said supplementaryconduit means and is operable to connect ysaid fourth electro-hydraulicvalve means to said pressure source.

16. A propeller as claimed in claim 14 further comprising a drainconduit, first duct means between said first and secondelectro-hydraulic valve means, second duct means between said secondelectro-hydraulic valve means and Asaid fourth electro-hydraulic valvemeans, third duct means between said fourth electro-hydraulic valvemeans and said reversing overriding means, wherein said firstelectro-hydraulic valve means comprises an electric solenoid energisableto actuate the valve means, a valve chamber, a first valve port in saidvalve chamber connected to the first auxiliary conduit means from thesource, a second valve port connected to drain conduit, a third valveport connected to the first auxliary conduit means leading to thecylinder of the piston and cylinder assembly, a fourth valve port, saidfirst duct means being connected to said fourth valve port, a valvemember in said valve chamber, said valve means being movable from afirst position in which it closes the first valve port to a secondposition in which it closes the second valve port, and spring means inoperative connection with said valve member urging said valve memberinto its said first position, said solenoid, when energised urging saidvalve member against the action of the spring into the second position,wherein said second electro-hydraulic valve means comprises an electricsolenoid energisable to actuate the valve means, a valve chamber, a rstvalve port connected to said first duct means which constitutes part ofsaid second auxiliary conduit means, a second valve port connected tothe drain conduit, a third valve port connected to said second auxiliaryconduit means leading to said relay, a fourth valve port, said fourthvalve port being connected to said second duct means and wherein saidfourth electro-hydraulic valve means comprises an electric solenoidenergisable to actuate the valve means, a valve chamber, a first valveport connected to said second duct means which forms part of saidsupplementary conduit means, a second valve port connected to the drainconduit, a third valve port connected to said third duct which formspart ofisaid supplementary conduit means, a valve member in said Valvecylinder, said valve means being movable from a first position in whichit closes the first valve port to a second position in which it closesthe second valve port, and spring means in operative connection withsaid valve member urging said valve member into its said first position,said solenoid, when energised urging said valve member against theaction of the spring into the second position.

17. in an aircraft `comprising a propeller-driving engine and means forvarying the speed of the engine operative connection therewith, apropeller as claimed 1n claim 14 in operative connection with said motorto be driven thereby wherein the first, second and fourthelectro-hydraulic Valve means each include a solenoid which whenactuated operates the electro-hydraulic valve, said propeller furthercomprising an electrical circuit including an electrical source ofelectrical current, a first relay switch, a first switch solenoid inoperative connection with said first relay switch and operable to opensaid switch, a second relay switch, a second switch solenoid inoperative connection with said second relay switch and operable to opensaid second relay switch, a propeller hub switch operatively connectedlo the said propeller blades and operable when said propeller bladesfine off to an amount less than a predetermined amount, first and secondsuperning switch means, a reversing switch means including two switchesoperatively interconnected so that when the first is open the second isclosed and in operative connection with said engine speed varying means,said reversing switch means being movable by said engine speed varyingmeans when the latter is moved to open said first reversing switch andto close the second reversing switch, said electric circuit furthercomprising rst, second and third line connections all connected inparallel to said electrical source, said first line connectionincorporating the solenoid of the second electro-hydraulic valve meansand said second relay switch in series therewith, the first switchsolenoid in parallel with said solenoid of the second electro-hydraulicvalve means and said second relay switch, said first superfining switchmeans in series with both of said solenoids, said second line connectionincorporating said first relay switch and the solenoid of a thirdelectro-hydraulic valve in series with said first relay switch, saidsecond superfining switch means, in series with said first reversingswitch and the second switch solenoid, said second superlining switchmeans, said first reversing switch and said second switch solenoidybeing connected in parallel with said first relay switch and thesolenoid of the third electro-hydraulic valve, said second lineconnection further incorporating said propeller hub switch in serieswith both said solenoids and said third line connection incorporatingsaid second reversing switch and the solenoid of the fourthelectro-hydraulic valve in connection therewith, hydraulically operablecoarsening overriding means movable into operative connection with saidhydraulic control valve to adjust the latter to connect said pressuresource to said coarse pitch conduit means, and supplementary hydraulicfluid conduit means between said pressure source and said coarseningoverriding means, said third electro-hydraulic valve in said secondsupplementary con- 21 duit means being operable to connect said pressuresource and said coarsening overriding means.

18. A variable pitch hydraulic propeller comprising a rotatable hub, aplurality of propeller blades supported on said hub, a pitch changemotor connected to the blades to vary the pitch of the blades, irst stopmeans operative to prevent the blades ning oli beyond a rst fine pitchposition, second stop means operative to prevent the blades lining offbeyond a second ne pitch position which is ner than the first ne pitchposition, rst Withdrawal means operable to render the rst stop meansinoperative, second Withdrawal means operable to render the second stopmeans inoperative and a hydraulic system comprising a source ofhydraulic pressure, a first conduit connecting the source with the rstwithdrawal means to operate said first Withdrawal means, a secondconduit separate from the rst conduit connecting the source with thesecond withdrawal means to operate said second Withdrawal means, rstvalve means in said rst conduit preventing connection between the sourceand the rst Withdrawal means when in its closed position, rst meansoperable to open the rst valve means, second valve means in said secondconduit preventing connection between the source and the secondWithdrawal means when in its closed position, and second means operableto open tne second valve means the rst and second means being connectedtogether to prevent operation of the second means before operation ofthe rst means.

References Cited in the tile of this patent UNITED STATES PATENTS2,477,868 Forman Aug. 2, 1949 2,542,463 Beard Feb. 20, 1951 2,600,017Morris June l0, 1952 2,609,057 Crowhurst Sept. 2, 1952 2,655,999 BaseviOct. 20, 1953 2,934,153 Chilman Apr. 26, 1960 FOREIGN PATENTS 672,953Great Britain May 28, 1952 742,148 Great Britain Dec. 2l, 1955

